Hydraulic control apparatus for endgates of trucks or the like

ABSTRACT

A control system for first and second double-acting hydraulic cylinders which respectively cause the endgate of a truck to pivot between open and closed positions and to move up or down. The flow of fluid into and from the lower chambers of the cylinders is controlled by discrete three-position twoway control valves, and the flow of fluid from the upper chamber of the first cylinder to a tank is controlled by an auxiliary valve assembly which acts as a pressure relief valve. If the endgate cannot displace the piston of the first cylinder due to its own weight, the auxiliary valve assembly is actuated to start a pump which delivers pressurized fluid to the upper chamber of the first cylinder. The upper chamber of the second cylinder can be connected directly to the tank or is connected with a line which conveys fluid from the upper chamber of the first cylinder to the auxiliary valve assembly.

United States Patent Herrmann et a1.

HYDRAULIC CONTROL APPARATUS FOR ENDGATES OF TRUCKS OR THE LIKE Inventors: Walter Herrmann, Vaihingen/Enz;

Heinrich Geisler, Gerlingen; Friedrich-Wilhelm Hofer, l-lofingen, all of Germany Robert Bosch GmbH, Stuttgart, Germany Filed: Sept. 7, 1973 Appl. No.: 395,372

Assignee:

Foreign Application Priority Data Sept. 11, 1972 Germany 2244445 3,736,845 6/1973 Weiste et a1. 60/D1G. 2

Primary Examiner-Edgar W. Geoghegan Attorney, Agent, or FirmMichael S. Striker [5 7] ABSTRACT A control system for first and second double-acting hydraulic cylinders which respectively cause the endgate of a truck to pivot between open and closed positions and to move up or down. The flow of fluid into and from the lower chambers of the cylinders is controlled by discrete three-position twoway control valves, and the flow of fluid from the upper chamber of the first cylinder to a tank is controlled by an auxiliary valve assembly which acts as a pressure relief valve. 1f the endgate cannot displace the piston of the first cylinder due to its own weight, the auxiliary valve assembly is actuated to start a pump which delivers pressurized fluid to the upper chamber of the first cyl inder. The upper chamber of the second cylinder can be connected directly to the tank or is connected with a line which conveys fluid from the upper chamber of the first cylinder to the auxiliary valve assembly.

16 Claims, 7 Drawing Figures PATENTE SEE H974 SHEET 1 UP 4 PATEHIE L181 71974 SHEET 2 OF 4 PATENTE 55171974 Fig 4 HYDRAULIC CONTROL APPARATUS FOR ENDGATES F TRUCKS on THE LIKE BACKGROUND-OF THE INVENTION The present invention relates to hydraulic control apparatus for one or more consumers, e.g., for one or more cylinder and piston units. More particularly,-the invention relates to improvements in hydraulic control apparatus of the type wherein at least one threeposition control valve serves to sea] at least one fluidconveying consumer line from a supply conduit as well as from a return conduit for hydraulic fluid in a first position of its valve member(s), wherein the control valve connects the consumer line with the supply conduit in a first operative position of its valve membe'r(s), and wherein the control valve connects the consumer line with the return conduit in a second operative position of its valve member(s).

it is already known to provide a hydraulic control apparatus with the just described control valve whose valve member(s) can regulate the flow of fluid to and from a single-acting consumer, and it is also known to provide such control apparatus with a control conduit wherein the flow of fluid is regulated by the control valve and which can supply fluid to a change-over valve serving to allow direct return flow of pressurized hydraulic fluid from the high-pressure outlet of a pump into a tank or a similar reservoir. Such control apparatus with poppet-type valves are normally used when the leakage of fluid must be reduced to a minimum, i.e., when the leakage should be less than that which takes place when using conventional valves with reciprocable spools or the like. A drawback of control apparatus with three-position two-way valves is that two such valves must be used in pairs if the apparatus is to regulate the flow of fluid to and from a double-acting consumer because each such valve can regulate the flow of fluid in a single fluid-conveying line. This contributes to the bulk, initial cost and maintenance cost of the control apparatus. Moreover the operation of actuating means for one of the valves must be accurately syn-' chronized 'with the operation of actuating means for the other valve, and this also contributes to the initial and maintenance cost of conventional control apparatus.

SUMMARY OF THE lNVENTlON An object of the invention is to provide a hydraulic control apparatus which can utilize a system of relatively simple control valves and other valves to regulate the flow of oil or another hydraulic fluid to and from one or more double-acting consumers of hydraulic fluid, for example, to and from the chambers of the double-acting cylinders one of which serves to pivot the endg'ate of a truck or trailer between open and closed positions and the other of which serves to move the endgate between upper and lower end positions.

Another object of the invention is to provide a control apparatus wherein excessive leakage of pressurized fluid is prevented or reduced to a minimum in a novel and improved way.

A further object of the invention is to provide a hydraulic control apparatus with novel and improved control valves for discrete double-acting consumers.

An additional object of the invention is to provide the control apparatus with a novel and improved auxiliary valve assembly which can regulate the flow of fluid in at least one fluid-conveying line of at least one doubleacting consumer.

Still another object of the invention is to provide a control apparatus which can regulate the flow of fluid to and from the chambers of a first double-acting consumer, independently of the flowof fluid to and from the chambers of at least one additional double-acting consumer.

An ancillary object of the invention is to provide a control apparatus which, though particularly suited to initiate and terminate movements of the endgate on an automotive vehicle or a trailer, can be used with equal advantage to effect and/or terminate the movements of any device or devices which are displaceable by one or more double-acting consumers in the form of cylinder and piston units or the like.

A further object of the invention is to provide a control apparatus wherein the motor for a pump or an analogous fluid pressurizing device is started and maintained in operation only when the double-acting consumer or consumers must overcome the resistance of one or more driven parts to movement between predetermined positions. I

The invention is embodied in a hydraulic control apparatus for one or more double-acting consumers (e.g., double-acting hydraulic cylinders which can move the endgate of a truck or the like between open and closed positions and between upper and lower end positions) wherein at least one control valve includes one or more valve members movable between first operative, second operative and neutral positions to thereby respectively connect (a) a first fluid-conveying line of the consumer with a supply conduit which is connected to a source of pressurized fluid, e.g., a pump and an electric motor for the pump, (b) with a return conduit which is connected to a tank or another suitable reservoir for hydraulic fluid, and (c) to seal the first line from the supply and return conduits, and wherein the valve members further regulate the flow of fluid in a control conduit for a switchover valve which opens in response to the flow of fluid in the control conduit from the supply conduit into the return conduit whereby the switchover valve provides a path for the flow of pressurized fluid in an additional conduit which connects the source with the tank.

The improvement in accordance with the present invention resides in the provision of auxiliary valve means which is installed in the additional conduit between the switchover valve and the tank to regulate the pressure of fluid in a second fluid-conveying line which connects the consumer or consumers with the additional conduit between the switchover valve and the auxiliary valve means. The auxiliary valve means may comprise a pressure relief valve whose valve member is held in an open position by suitable detent means and can be moved to a closed position by actuating means 7 which can thereby complete the circuit of the motor to start the pump as soon as the pressure relief valve is closed.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved hydraulic control apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain BRIEF DESCRIPTION. OF THE DRAWING FIG. 1 is a diagrammatic viewof a hydraulic control apparatus for the endgate of a truck;

FIG. 2 is a diagrammatic view of a portion of a second control apparatus;

FIG. 3 is a diagrammatic view of a third control apparatus; 2

FIG. 4 is a diagrammatic view of a fourth control apparatus;

FIG. 5 is an axial sectional view of a directional control valve in the apparatus of FIG. 4;

FIG. 6 is a'fragmentary diagrammatic view of a control apparatus which constitutes a first modification of the apparatus shown in FIG. 4; and

FIG. 7 is a fragmentary diagrammatic view of a control apparatus which constitutes a second modification of the apparatus shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a hydraulic control apparatus 11 for two discrete consumers in the form of cylinders 12, 13 which impart various movements to the endgate G of a truck, station wagon or an analogous automotive vehicle. The cylinder 12 is of the double-acting type and serves to pivot the gate G between open and closed positions (arrow 9), and the cylinder 13 is a single-acting hydraulic jack which can raise the gate G (arrow from a lower end position in which the gate is close to the ground to an upper end position in which the gate is ready to be pivoted to its closed position. The gate G descends under its own weight when the control apparatus 11 allows fluid to escape from the lower chamber 42 of the cylinder 13.

The control apparatus 11 comprises a block-shaped housing 14 which includes a connecting plate 15 adapted to be secured to the dashboard or to another part of the vehicle,.anend plate 18, and two identical I control valves 16, 17 here shown in the form of directional control valves eachof which has two valve membe rs or spools. The details of a slightly modified'control valve are illustrated in FIG. 5. The control valves 16, 17 are connected in parallel between a supply conduit 19 for pressurized oil or another hydraulic fluid and a return conduit for hydraulic fluid. The valve members or spools of each of the control valves 16, 17 are movable between central or neutral positions 22 (which are determined by suitable resilient biasing means) and two operative positions 24, 5. When in the central positions 22, the valve spools of the control valve 17 seal the conduits 19, 21 from a first fluid-conveying line or consumer line 23 which is connected with the lower chamber 40 of the cylinder 12 by a further fluid conveying line or consumer line 39. When in the central positions 22, the valve spools of the control valve 16 seal the conduits 19, 21 from a first fluid-conveying line or consumer line 41 which is connected with the lower chamber 42 of the cylinder 13. When in the first operative positions 24, the valve spools of the control valves 16, 17 respectively connect the supply conduit 19 with the consumer lines 41, 23. When in the second operative positions 25, the valve spools of the control valves 16, 17 respectively connect the return conduit 21. with the consumer lines 41, 23. The valve spools of the control valves 16, 17 are movable by discrete mechanical actuating means 26, and each actuating means 26 comprises a cam or trip 27 for a normally open limit switch 28. When a limit switch 28 is closed (in the first operative positions 24 of the respective valve spools), an electric motor 36 or an analogous prime mover drives a pump 35 which constitutes a source of pressurized hydraulic fluid. v

The connecting plate 15 supports or embodies'a pressure relief valve 29 which opens automatically when the pressure of fluid in the supply conduit 19 rises to a predetermined maximum permissible value and then allows pressurized fluid to flow from the supply conduit 19into the return conduit 21 and thence into a reservoir or tank 37. Furthermore, the connecting plate 15 supports a conventional switchover valve 32 which is connected to the supply conduit 19 by a bypass conduit 31. A control conduit 33 connects the bypass conduit 31 with the return conduit 21 and the flow of fluid therein is regulated by the control valves 16 and 17. A portion of the control conduit 33 extends through the end plate 18 of the housing 14. When the control conduit 33 is allowed by control valves 16, 17 to convey fluid from the conduit 31 to the conduit 21, it maintains the switchover valve 32 in open position.

The inlet of the supply conduit 19 is connected with the tank 37 by a conduit 34 which contains the pump 35. The connection between the tank 37 and the return conduit 21 comprises a further conduit 38.

The consumer line 39 admits pressurized hydraulic fluid to the lower chamber 40 of the cylinder 12 when the piston rod 12a is to pivot the gate G to its closed position. The upper chamber 46 of the cylinder 12 then discharges fluid by way of a second fluid-conveying or working line which is connected to an additional conduit 43. The latter is connectable to the bypass conduit 31 by the switchover valve 32. The upper chamber 47 of the cylinder 13 is connected with the tank 37 by a fluid-conveying or working line 48. The chamber 47 discharges fluid when thechamber 42 of the cylinder 13 receives pressurized fluid for the purpose of moving the gate G from the lower to the upper end position.

The additional conduit 43 is connected with the tank 37 and contains an auxiliary valve assembly 44 which constitutes a pressure relief valve having a valve member 51 which is biased by a spring 49. The valve member 51 can be displaced by mechanical actuating means 52 which can be held in a selected position by a detent device 53. A cam 54 on the actuating means 52 constitutes a trip for an electric switch 55 which can open or complete the circuit of the electric motor 36 for the pump 35.

The operation of the control apparatus 11 is as follows:

It is assumed that the gate G dwells in the upper end position (i.e., that the piston 13b has been moved to its upper end position) and that the gate is closed (i.e., that the piston 12b is also held in its upper end position). In order to move the gate G to, its open (horizontal or substantially horizontal) position, the actuating means 26 is caused to move the valve spools of the control valve 17 to the operative positions 25 in which the consumer lines 23, 39 connect the chamber 40 of the cylinder 12 to the return conduit 21. The trip 27 does not close the respective limit switch 28 so that the motor 36 for the pump 35 remains idle. The valve member 51 of the auxiliary valve assembly 44 is held in open position by the detent device 53. The weight of the gate G causes the piston rod 12a to move downwardly and to expel fluid from the chamber 40 whereby such fluid flows into the tank 37 via consumer lines 39, 23, valve 17 and conduits 21, 38. At the same time, the descending piston 12b sucks hydraulic fluid into the chamber 46 via additional conduit 43, open valve member 51 and working line 45.

If the vehicle is driven or is at a standstill on a downwardly inclined slope so that the weight of the gate G cannot move the piston rod 12a downwardly, the piston 12b does not descend even though the valve spools of the valve 17 assume the second operative positions and the valve member 51 of the auxiliary valve assembly 44 is open. The operator then moves the actuating means 52 against the opposition of the detent device 53 whereby the trip 54 closes the switch 55 which starts the motor 36 for the pump 35. The pump delivers pressurized hydraulic fluid to the conduits 34, 19 and 31 whereby the fluid entering the bypass conduit 31 flows into the tank 37 through the switchover valve 32, additional conduit 43 and auxiliary valve assembly 44. The switchover valve 32 is open because the control conduit 33 communicates with the return conduit 21 when the valve spools of the valve 17 assume the second end positions 25. Depending on the setting of the valve assembly 44, the latter throttles the flow of fluid from the additional conduit 43 into the tank 37 to a selected extent whereby the pressure of fluid in the additional conduit 43 (upstream of the valve member 51) and in the working line 45 rises. Such pressure is communicated to fluid in the chamber 46 so that the piston 12b descends and the gate G is pivoted to the open position. Thus, the gate G can be pivoted to open position by gravity alone or in response to starting of the motor 36 on movement of the actuating means 52 to a position in which the trip 54 closes the electric switch 55.

If the gate G is to be returned to the closed position, the valve spools of the control valve 17 are moved to the operative positions 24 by the respective actuating means 26. This causes the trip 27 of such actuating means 26 to close the associated limit switch 28 which starts the motor 36 for the pump 35. The control valve 17 seals the control conduit 33 from the return conduit 21 so that the switchover valve 32 is closed; therefore, the pump 35 feeds pressurized fluid to the supply conduit 19 and into the chamber through the consumer lines 23, 39. The fluid which is expelled from the chamber 46 by the piston 12b flows into the tank 37 via working line 45, and the open valve member 51 of the valve assembly 44. it is assumedhere that the detent device 53 maintains the valve member 51 in the open position against the opposition of the spring 49.

The flow of hydraulic fluid into and from the chambers 42, 47 of the cylinder 13 can'be regulated independently of the cylinder 12. The valve spools of the valve 16 are moved to the first operative positions 24 for lifting and to the second operative positions 25 for lowering of the gate G. The lowering of the gate G can take place due to the fact that the weight of the gate rests on the piston rod 130 of the piston 13b in the cylinder 13; therefore. the motor 36 for the pump 35 is started only when the operator desired to move the gate G to the upper end position. Thus, the trip 27 of the actuating means 26 for the valve spools of the control valve 16 will close the associated limit switch 28 only when the actuating means 26 moves such valve spools to the positions 24. The control valve 16 then seals the control conduit 33 from the return conduit 21 so that the switchover valve 32 is closed.

The auxiliary valve assembly 44 limits the pressure of hydraulic fluid in such a way that the gate G cannot lift the vehicle off the ground during movement to open position. On the other hand, the pressure relief valve 29 determines the upper limit of the much higher fluid pressure which is needed to pivot the gate G to the closed position or to raise the gate from the lower to the upper end position.

The actuating means 52 for the valve member 51 of the valve assembly 44 can be manipulated independently of the actuating means 26 for the valve spools of the control valve 17. However, these actuating means may be coupled to each other if the mounting of the gate G on the vehicle is such that the weight of the gate always opposes its movement toward the open position. This means that the switch 55 is closed in automatic response to movement of the valve spools of the control valve 17 to the operative positions 25 in which the control valve 17 initiates the pivotal movement of gate G toward its open position.

The provision of auxiliary valve assembly 44 in the additional conduit 43 and the mounting of such valve assembly between the switchover valve 32 and tank 37 constitutes an important feature of the improved control apparatus. Another feature of the control apparatus resides in the provision of the fluid-conveying working line 45 which connects the upper chamber 46 of the cylinder 12 with the additional conduit 43 between the switchover valve 32 and auxiliary valve assembly 44. These features enable the apparatus to employ control valves (16 and 17) which, in heretofore known control apparatus, can be used to regulate the flow of fluid between supply and return conduits on the one hand and single-acting consumers on the other hand. The sealing action of control valves 16 and 17 is highly satisfactory.

The valve member 51 of the auxiliary valve assembly 44 can be moved to open position at the will of the operator to thereby allow the fluid to flow from the charnber 46 into the tank 37. Moreover, the valve assembly 44 can throttle the flow of fluid to a desired extent to thereby control the speed of movement of the gate G to its open position. The feature that the motor 36 is started only when necessary because the load (e.g., the gate G) cannot depress the piston 12b due to its own weight is particularly advantageous when the hydraulic control apparatus is used in or on vehicles which do not have unlimited sources of electrical energy.

In the control apparatus of FIG. 1, the cylinder 13 acts as a single-acting cylinder because the pump 35 cannot supply pressurized fluid into the upper chamber 47. Thus, the piston 13b descends only under the weight of the load G.

FIG. 2 illustrates a modified auxiliary valve assembly which can be used in the additional conduit 43 of the control apparatus 11 of FIG. 1 as a substitute for the auxiliary valve assembly 44. The valve assembly 60 comprises a two-position two-way solenoid-operated valve 61 and a pressure relief valve 62 which is connected in parallel with the valve 61. The valves 61, 62 are of the commercially available type. The solenoid 61b of the valve 61 is energized by the actuating means 26 of the control valve 17 when the valve spools of the control valve 17 assume the operative positions 25 for movement of the gate G to its open position. In all other respects, the operation of the control apparatus which embodies the auxiliary valve assembly 60 is identical with that of the control apparatus 11. The spring 61a of the two-way valve 61 serves as a means for yieldably biasing the valve member (not shown) of the valve 61 to an open position. The valve member of the valve 61 is moved to a closed position in which it seals the additional conduit 43 when the solenoid 61b is energized in response to closing of the limit switch 28 which is associated with the control valve 17.

Referring to FIG. 3, there is shown a hydraulic control apparatus 70 which differs from the control apparatus 11 of FIG. 1 in the following respects:

The additional conduit 43 contains a conventional adjustable pressure relief valve 71 and is connected with the chambers 46, 47 of the cylinders 12, 13 by a second fluid-conveying or working line 72. The junction between the additional conduit 43 and working line 72 is located between the valves 32 and 71. The valve 71 is connected in parallel with a check valve 73 which is installed in an additional fluid-conveying line 73a connecting the working line 72 with the additional conduit 43 (i.e., with the tank 37) downstream of the valve 71. The valves 71, 73 together constitute an auxiliary valve assembly replacing the assembly 44 of FIG. 1.

Another difference between the control apparatus 11 and 70 is that the actuating means 26 (not shown) of the control valves l6, 17 of FIG. 3 close the respective limit switches 28 (not shown) in both operative positions (24, 25) of the corresponding valve spools. For example, the trips which serve to close the limit switches 28 during opening and during lowering of the gate G are preferably designed to start the pump motor 36 with a certain delay following the movement of the valve spools of the control valve 16 or 17 to the operative positions 25. Thus, the pump 35 is not started in automatic response to movement of the valve spools of control valve 16 or 17 to the operative positions 25; if the weight of the gate G cannot initiate a pivotal movement to open position or a lowering of the gate, the motor 36 is started with a certain delay and thereupon causes the pump 35 to effect an opening or lowering of the gate G in a manner as described in connection with FIG. 1. Such delayed starting of the motor 36 reduces the energy requirements of the control apparatus 70 and contributes to simplicity of its construction and mode of operation.

The differences between the modes of operation of the control apparatus 11 and 70 are as follows:

If the pump 35 of the control apparatus 70 would feed a pressurized hydraulic fluid in the neutral positions 22 of the valve spools of the control valve 16 or 17, the throttling action of the pressure relief valve 71 would raise the fluid pressure in the additional conduit 43 and hence in the chambers 46, 47 of the cylinders l2, 13 (via working line 72). When the valve spools of the control valve 17 assume the operative positions 24 (to initiate the movement of gate G to the closed position), the flow of fluid which is being expelled from the chamber 46 is throttled in the valve 71. The fluid pressure which is selected by the setting of valve 71 is only a small fraction (e.g., one seventh) of the pressure at which the relief valve 29 opens. Therefore, the force which is available for closing the gate G depends on the differential between the fluid pressures in the chambers 40, 46 and the difference in effective areas of the upper end lower surfaces of the differential piston 12b in the cylinder 12. This also applies for the cylinder 13 whose chamber 42 receives pressurized fluid when the piston rod 13a is to move the gate G to the upper end position.

An important advantage of the control apparatus is that fluid which is expelled from the chamber 46 during closing of the gate G can flow in the working line 72 and into the chamber 47 of the cylinder 13. Thus, if the valve spools of the control valve 16 are moved to the operative positions 25 (lowering of the gate G) while the valve 71 throttles the flow of fluid from the line72 into the tank 37, the gate G can descend due to its weight as well as in response to fluid pressure in the chamber 47. This also applies when the chamber 42 of the cylinder 13 receives fluid while the chamber 40 of the cylinder 12 is free to communicate with the return conduit 21. If the gate G is to pivot toward open position exclusively owing to its weight while the pump 35 is at a standstill, the piston 12b of the cylinder 12 can draw fluid from the tank 37 into the chamber 46 through the check valve 73 and lines 73a, 72. The pressure relief valve 71 need not be associated with an electric switch for the motor 36.

It will be noted that each of the cylinders l2, 13 can act as a double-acting cylinder even though they are controlled by valves l6, 17 which are normally used for single-acting consumers.

FIG. 4 illustrates a control apparatus which differs from the control apparatus 70 of HG. 3 in that the maximum fluid pressure is available to move the pistons 12b, 13b in the cylinders 12 and 13. The differences between the control apparatus 11 and 80 are as follows:

The plate 15 is connected or integral with a second end plate 81 for a second switchover valve 82. The valve 82 opens in response to the flow of fluid in a second control conduit 83 which extends in parallelism with the control conduit 33 and wherein the flow of fluid is regulated by the control valves 16 and 17. A portion of the second control conduit 83 extends through the end plate 18 and communicates with the return conduit 21. The flow of fluid in the control conduit 83 is unobstructed in the neutral positions 22 of valve spools in the control valves 16, 17. The control conduits 33, 83 are respectively open and closed in the operative positions 24 of valve spools in the control valves 16, 17 and are respectively closed and open in the operative positions 25 of such valve spools.

The end plate 81 further supports a second pressure relief valve 84 which is connected in parallel with the pressure relief valve 29 and switchover valve 82. The chambers 46, 47 of the cylinders 12, 13 are connected with a fluid-conveying or working line 85 which communicates with the additional conduit 43 between the switchover valves 32, 82. A check valve 86 for the cylinders 12, 13 is installed in an additional fluidconveying line 86 which connects the working line 85 with the additional conduit 43 between the tank 37 and switchover valve 82. The limit switches 28 are closed with a delay following the movement of respective valve spools (in the control valves 16, 17) to the second operative positions 25.

The operation of the control apparatus 80 differs from the operation of the control apparatus 70 in the following respects:

When the control valve 17 admits pressurized fluid from the pump 35 into the chamber 40 of the cylinder 12 to thereby pivot the gate G toward the closed position, the switchover valve 32 is closed and the second control conduit 83 is open. The fluid which flows from the chamber 46 flows into the tank 37 (via working line 85 and switchover valve 82) practically without any throttling action. This is due to the fact that the stream of fluid in the control conduit 83 maintains the second switchover valve 82 in open position.

If the chamber 40 of the cylinder 12 discharges fluid in order to allow the gate G to pivot toward its open position, the valve spools of the control valve 17 assume the operative positions 25 so that fluid escaping from the chamber 40 can enter the return conduit 21. The pump 3 5 is idle and the piston 12b draws fluid from the tank 37 into the chamber 40 via check valve 86 and lines 860, 85. If the gate G can move to open position only in response to admission of pressurized fluid into the chamber 46, the limit switch 28 which is associated with the actuating means 26 of the control valve 17 starts the motor 36 for the pump 35. Since the flow of fluid in the control conduit 33 is unobstructed, the switchover valve 32 is open but the second switchover valve 82 is closed because the control valve 17 seals the second control conduit 83. The pressurized fluid which is supplied by the pump 35 flows through the pressure relief valve 84 and its pressure is available in the chamber 46 via working line 85.

It will be seen that the maximum pressure of fluid is available for operation of the cylinder 12 or 13 (such maximum pressure is determined by the relief valve 29). When the cylinders 12, 13 are operated simultaneou'sly but in opposite directions, fluid which flows from one of the cylinders 12, 13 and through the working line 85 is throttled by the relief valve 84 and the pressure of such fluid opposes the maximum fluid pressure in one of the cylinders 12, 13.

The valves 82, 84, 86 constitute an auxiliary valve assembly which replaces the valve assembly 44 of FIG; 1 and whose valves are connected in parallel to each other. The control conduit 83 connects the return conduit 21 with the additional conduit 43 between the switchover valves 32, 82.

FIG. 5 illustrates the details of the control valve 16 in the control apparatus 80 of FIG. 4. The control valve 16 has a body 90 for two reciprocable valve spools 91, 92 which can be moved lengthwise by the actuating means 26. The valve spool 91 controls the flow of hydraulic fluid between the supply conduit 19 and the consumer line 23; this spool has a plunger 93 which regulates the flow of fluid in the control conduit 33. The spool 92 controls the flow of fluid between the consumer line 23 and the return conduit 21', this spool also comprises a plunger, shown at 94, which regulates the flow of fluid in the second control conduit 83. The positions of spools 91, 92 which are shown in FIG. 5 are their neutral positions (22). The actuating means 26 comprises a lever 95 which must be pivoted in a clockwise direction, as viewed in FIG. 5, to move the spools 91, 92 to their first operative positions (24). The lever 95 must be pivoted counterclockwise in order to move the spools 91, 92 to the second operative positions (25). In such second operative positions, the spools 91,

16 in a manner as shown in FIG. 4.

Referring to FIG. 6, there is shown a portion of a further control apparatus 100 which differs from the control apparatus of FIG. 4 in that it comprises a different second control conduit 101. The control conduit 101 contains a two-position, two-way solenoidoperated valve 102 and sine the flow of fluid therein is not regulated by the control valves 16 and 17; it can be connected directly to the tank 37. The valve 102 is normally open and is closed by a limit switch 28 in response to movement of valve spools in one of the control valves 16, 17 to the second operative position 25. Otherwise, the operation of the control apparatus is identical with that of the control apparatus 80.

FIG. 7 shows a portion of still another control apparatus which differs from the control apparatus 80 of FIG. 4 in that it further comprises a deactivatable check valve 111 which is caused by a' switchover valve 112 to permit hydraulic fluid to flow from the working line 85 into the additional conduit 43 in response to flow of fluid through the control conduit 33 or 83. This renders it possible to prevent the flow of fluid from the cylinders 12, 13 in one direction by the control valves 16, 17 and in another direction by the check valve 111. The provision of check valve 111 is desirable because the switchover valves 32, 82 are normally of the type having a reciprocable spool and, therefore, they cannot reliably prevent the flow of fluid therethrough;

The operation of the control apparatus 110 is practica'lly identical with that of the control apparatus 80. When the valve spools of the control valve'16 or 17 assume the first operative positions 24, the valve 112 opens the check valve 111. When the valve spools of the control valve 16 or 17 assume the second operative positions 25, the gate G (not shown in FIG. 7) pivots toward itsopen position or moves toward the lower end position due to its own weight or forcibly, i.e., with the assistance from fluid which is supplied by the pump 35. The control apparatus 110 operates with substantial savings in energy and with a relatively simple changeover valve because the gate G can descend due to its own weight and, therefore, it is not necessary to use pressurized fluid to open the changeover valve.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. In a hydraulic control apparatus for at least one double-acting. consumer wherein at least one control valve includes at least one valve member movable between first operative, second operative and neutral positions to thereby respectively connect a first fluidconveying line of said consumer with a supply conduit which is connected to a source of pressurized fluid, with a return conduit which is connected to a tank, and to seal said first line from said conduits, and wherein said valve member regulates the flow of fluid in a control conduit for a switchover valve which opens in response to fluid flow in said control conduit to thereby provide a path for the flow of pressurized fluid in an additional conduit connecting said source to said tank, the improvement which consists in the provision of auxiliary valve means installed in said additional conduit between said tank and said switchover valve to regulate the pressure of fluid in a second fluid-conveying line which connects said consumer with said additional conduit between said switchover valve and said auxiliary valve means.

2. Theimprovement as defined in claim 1, wherein said auxiliary valve means comprises a pressure relief valve having a valve member movable between open and closed positions, detent means for yieldably holding said last mentioned valve member in at least one of said positions, and actuating means for moving said last mentioned valve member between said positions.

3. The improvement as defined in claim 1, wherein said auxiliary valve means comprises a two-position two-way valve and a pressure relief valve in parallel with said two-way valve, said two-way valve having a valve member movable between open and closed positions and means for yieldably biasing said last mentioned valve member to said open position.

4. The improvement as defined in claim 1, wherein said auxiliary valve means comprises a pressure relief valve and a check valve connected in parallel with said pressure relief valve, said check valve being arranged to prevent the flow of fluid from said consumer to said tank in a further fluid-conveying line connecting said tank with said second line.

5. The improvement as defined in claim 1, wherein said source comprises a pump and electric motor means for said pump, said auxiliary valve assembly comprising a pressure relief valve having a valve member movable between open and closed positions, detent means for yieldably holding said last mentioned valve member in at least one of said positions, actuating .means for moving said last mentioned valve member between said positions, and electric switch means for completing the circuit of said motor means in response to movement of said last mentioned valve member to said open position.

6. The improvement as defined in claim 5, wherein said actuating means comprises means for closing said switch means.

7. The improvement as defined in claim 1, comprising two double-acting consumers and discrete first and second control valves for said consumers, said second line being connected with both said consumers.

8. The improvement as defined in claim 7, wherein said auxiliary valve means comprises a second switchover valve provided in said additional conduit between said first mentioned switchover valve and said tank and arranged to open in response to the flow of fluid in a second control conduit which connects said additional conduit between said switchover valves with said return conduit and wherein the flow of fluid is regulated by said control valves, said auxiliary valve means further comprising a pressure relief valve connected in parallel with said second switchover valve and a check valve also connected in parallel with said second switchover valve and installed in an additional fluid conveying line connecting said second line with said tank.

9. The improvement as defined in claim, 8, wherein each of said control valves comprises a plurality of valve members one of which regulates the flow of fluid in said second control conduit and the flow of fluid from the respective first line into said return conduit.

10. The improvement as defined in claim 8, further comprising a check valve in said second fluidconveying line and means for operatively connecting said check valve with said control conduits so as to open said check valve for the flow of fluid from said consumers in response to the flow of fluid in one of said control conduits.

11. The improvement as defined in claim 1, wherein said source comprises a pump and an electric motor for said pump, said control valve comprising actuating means for moving said valve member between said positions and electric switch means for completing the circuit of said motor in at least one position of said valve member.

12. The improvement as defined in claim 1 1, wherein said actuating means comprises means for closing said switch means in said one position of said valve member.

' 13. The improvement as defined in claim 1, comprising two double-acting consumers and discrete first and second control valves for said consumers, said second line being connected with both said consumers and said auxiliary valve means comprising a second switchover valve installed in said additional conduit between said tank and said first mentioned switchover valve, a pressure relief valve connected in parallel with said second switchover valve and a check valve connected in parallel with said second switchover valve and installed in an additional fluid-conveying line connecting said second line with said tank; and further comprising a second control conduit connecting said tank with said additional line between said switchover valves and a solenoid-operated valve provided in said second control conduit and arranged to seal said second control conduit in the second operative position of said valve member, said second switchover valve being arranged to open in response to the flow of fluid in said second control conduit.

14. The improvement as defined in claim 1, further comprising a gate, said consumer having means for changing the position of said gate at least in response to connection of said first line with said supply conduit.

15. The improvement as defined in claim 14, wherein said source comprises a pump and an electric motor for said pump, said control valve comprising means for completing the circuit of said motor in at least one position of said valve member.

16. The improvement as defined in claim 14, wherein said source comprises a pump and an electric motor for said pump, said auxiliary valve means comprising means for completing the circuit of said motor. 

1. In a hydraulic control apparatus for at least one doubleacting consumer wherein at least one control valve includes at least one valve member movable between first operative, second operative and neutral positions to thereby respectively connect a first fluid-conveying line of said consumer with a supply conduit which is connected to a source of pressurized fluid, with a return conduit which is connected to a tank, and to seal said first line from said conduits, and wherein said valve member regulates the flow of fluid in a control conduit for a switchover valve which opens in response to fluid flow In said control conduit to thereby provide a path for the flow of pressurized fluid in an additional conduit connecting said source to said tank, the improvement which consists in the provision of auxiliary valve means installed in said additional conduit between said tank and said switchover valve to regulate the pressure of fluid in a second fluid-conveying line which connects said consumer with said additional conduit between said switchover valve and said auxiliary valve means.
 2. The improvement as defined in claim 1, wherein said auxiliary valve means comprises a pressure relief valve having a valve member movable between open and closed positions, detent means for yieldably holding said last mentioned valve member in at least one of said positions, and actuating means for moving said last mentioned valve member between said positions.
 3. The improvement as defined in claim 1, wherein said auxiliary valve means comprises a two-position two-way valve and a pressure relief valve in parallel with said two-way valve, said two-way valve having a valve member movable between open and closed positions and means for yieldably biasing said last mentioned valve member to said open position.
 4. The improvement as defined in claim 1, wherein said auxiliary valve means comprises a pressure relief valve and a check valve connected in parallel with said pressure relief valve, said check valve being arranged to prevent the flow of fluid from said consumer to said tank in a further fluid-conveying line connecting said tank with said second line.
 5. The improvement as defined in claim 1, wherein said source comprises a pump and electric motor means for said pump, said auxiliary valve assembly comprising a pressure relief valve having a valve member movable between open and closed positions, detent means for yieldably holding said last mentioned valve member in at least one of said positions, actuating means for moving said last mentioned valve member between said positions, and electric switch means for completing the circuit of said motor means in response to movement of said last mentioned valve member to said open position.
 6. The improvement as defined in claim 5, wherein said actuating means comprises means for closing said switch means.
 7. The improvement as defined in claim 1, comprising two double-acting consumers and discrete first and second control valves for said consumers, said second line being connected with both said consumers.
 8. The improvement as defined in claim 7, wherein said auxiliary valve means comprises a second switchover valve provided in said additional conduit between said first mentioned switchover valve and said tank and arranged to open in response to the flow of fluid in a second control conduit which connects said additional conduit between said switchover valves with said return conduit and wherein the flow of fluid is regulated by said control valves, said auxiliary valve means further comprising a pressure relief valve connected in parallel with said second switchover valve and a check valve also connected in parallel with said second switchover valve and installed in an additional fluid conveying line connecting said second line with said tank.
 9. The improvement as defined in claim 8, wherein each of said control valves comprises a plurality of valve members one of which regulates the flow of fluid in said second control conduit and the flow of fluid from the respective first line into said return conduit.
 10. The improvement as defined in claim 8, further comprising a check valve in said second fluid-conveying line and means for operatively connecting said check valve with said control conduits so as to open said check valve for the flow of fluid from said consumers in response to the flow of fluid in one of said control conduits.
 11. The improvement as defined in claim 1, wherein said source comprises a pump and an electric motor for said pump, said control valve comprising actuating means for moving sAid valve member between said positions and electric switch means for completing the circuit of said motor in at least one position of said valve member.
 12. The improvement as defined in claim 11, wherein said actuating means comprises means for closing said switch means in said one position of said valve member.
 13. The improvement as defined in claim 1, comprising two double-acting consumers and discrete first and second control valves for said consumers, said second line being connected with both said consumers and said auxiliary valve means comprising a second switchover valve installed in said additional conduit between said tank and said first mentioned switchover valve, a pressure relief valve connected in parallel with said second switchover valve and a check valve connected in parallel with said second switchover valve and installed in an additional fluid-conveying line connecting said second line with said tank; and further comprising a second control conduit connecting said tank with said additional line between said switchover valves and a solenoid-operated valve provided in said second control conduit and arranged to seal said second control conduit in the second operative position of said valve member, said second switchover valve being arranged to open in response to the flow of fluid in said second control conduit.
 14. The improvement as defined in claim 1, further comprising a gate, said consumer having means for changing the position of said gate at least in response to connection of said first line with said supply conduit.
 15. The improvement as defined in claim 14, wherein said source comprises a pump and an electric motor for said pump, said control valve comprising means for completing the circuit of said motor in at least one position of said valve member.
 16. The improvement as defined in claim 14, wherein said source comprises a pump and an electric motor for said pump, said auxiliary valve means comprising means for completing the circuit of said motor. 